Fibers made from cyanato group containing phenolic resins, and phenolic triazines resins

ABSTRACT

The present invention is a fiber comprising cyanato group containing phenolic resin comprising repeating units of the formula: ##STR1## wherein p is 0 or an integer of one or more, q is 0 or an integer of 1 or more, X is a radical selected from the group consisting of: --CH 2  --, --CO--, --SO 2  --, ##STR2## and R is the same or different and is selected from the group consisting of hydrogen and methyl radicals. The fiber of the present invention can be made a phenolic triazine derived from the cyanato group containing phenolic resin.

The present invention is in the field of fibers made from phenol basedresins. More particularly, the present invention relates to fibers madeof cyanato group containing phenolic resin, also known as phenoliccyanate resin, a method to prepare the fibers, and fibers made fromtriazine resins.

Cyanato group containing phenolic resins have been described in U.S.Pat. Nos. 3,448,079 and 4,022,755 as well as in Delano, et al, Synthesisof Improved Phenolic Resins, Acurex Corp/Aerotherm, Acurex Vinyl Report79-25/AS, Sept. 4, 1979 prepared for NASA Lewis Research Center,Contract No. Nas3-21368, and is available through the U.S. Department ofCommerce National Technical Information Service.

A recent reference, Heat Resistance Polymers by Critchley, et al, pp.406-408 Plenum Press, New York, 1986 has described phenolic triazineresins prepared from phenolic novolac or meta-cresol novolac which haveessentially the same chemical structures as described in the abovereferenced patents.

The phenolic triazines which have been disclosed have been found to havehigh thermal stability. Copending U.S. Ser. No. 104,700 filed Oct. 5,1987, hereby incorporated by reference discloses cyanato groupcontaining phenolic resins and phenolic triazines. The cyanato groupcontaining phenolic resins are disclosed to be stable as measured by geltime. The phenolic triazine resins are disclosed to be thermally stableas measured by Thermal Gravimetric Analysis.

Crosslinked phenolic resin fibers are disclosed in the art. Hayes, S.L., "Novoloid Fibers", Kirk-Othmer, Encyclopedia of Chemical Technology,volume 16, pages 125-138 (John Wiley and Sons, Inc., 1981) disclosesnovoloid fibers as crosslinked phenolic-aldehyde fibers typicallyprepared by acid-catalyzed cross-linking of a melt-spun novolac resinwith formaldehyde.

Phenol formaldehyde or novoloid fibers were invented by Dr. JamesEconomy and coworkers at Carborundam Company in the late 1960s and early1970s (U.S. Pat. No. 3,650,102) at present, Nippor Kynol, Inc, in Japanand American Kynol (New York) manufacture and sell novoloid fibers underthe tradename Kynol.

Production of state of the art phenolic fiber involves basic phenoliccuring chemistry. Typically, fiber is produced by melt-spinning anovolac resin and then curing the resulting precursor fibers in anacidic, aqueous solution of formaldehyde to effect crosslinking. Duringthe processing it generates volatile by products, which ultimatelydiffuse into the skin on fiber surface and produce mechanically weakfiber. The ideal crosslinked phenolic fiber represented as: ##STR3##

Kynol fibers are the only commercially available novoloid fibers, andare used in a wide variety of flame and chemical-resistant textiles andpapers, in composites, gaskets, and friction materials, and asprecursors for carbon and activated-carbon fibers, textiles andcomposites Novoloid fibers are highly flame resistant, but are not hightemperature fibers. The temperature stability of novolac fiber islimited because of oxidative decomposition of mehtylene bridge leadingto punking (afterglow) upon expositure to a flame. ##STR4##Decomposition of the peroxide formed at the methylene linkage is anexothermic reaction and leading to significant loss of weight andstrength as temperatures approach 200° C.

U.S. Pat. No. 4,076,692 discloses a process for manufacturing novaloidfiber. This patent generally discloses forming a cured novolac fiberwhich comprises blending uncured novolac resin with a novolaccrosslinking agent at a temperature below the curing temperature of theresulting blend. The process further comprises melting a portion of theresulting blend at a temperature of from 125° to 500° C. and fiberizingthe melted portion before the melted portion cures to an extent whichprevents such fiberizing. The resulting fibers are cured by contactingthem with acidic gas at from 20° to 300° C. and from about 1 to about 10atmospheres of pressure.

During the processing of conventional phenolic fibers volatilebyproducts are generated which can diffuse into the skin on the fibersurface and produce mechanically weak fiber. Presently such novaloidfibers are commercialized in a wide variety of flame and chemicalresistant textiles and papers. They are used in composites gaskets andfriction materials. They are also used as precursors for carbon andactivated carbon fibers, textiles and composites. While novaloid fibersare highly flame resistant they are not high temperature fibers. Thetemperature stability of novalac fiber is limited because of oxidativedecomposition of the methyl bridge between the phenol groups. Thisresults in the significant loss of weight and strength as temperaturesapproach 200°C.

SUMMARY OF THE INVENTION

The present invention is a fiber comprising a cyanato group containingphenolic resin. The cyanato group containing resin (phenolic cyanateresin) is derived from a phenolic resin of the comprising repeating unitof the formula I: ##STR5## wherein n is 0 or an integer of one or more,and X is a radical selected from the group consisting of: --CH₂ --,--CO--, --SO₂ --, ##STR6## R is the same or different and is selectedfrom the group consisting of hydrogen and methyl radicals.

The cyanato group containing phenolic resin is derived from the phenolicresin (formula I) and has repeating units of the formula II ##STR7##wherein p is 0 or an integer of one or more,

q is 0 or an integer of one or more, and

X and R are defined as in formula I.

There is from 10 to 100 mole percent, preferably 50 to 100 mole percent,more preferably 80 to 100 mole percent and most preferrably 85 to 100percent of the cyanate units. The phenolic units and cyanato units canbe distributed in any order, including random or block distributionalong the polymer chain.

A preferred phenolic cyanate useful to make fibers has the formula III##STR8## wherein Z is selected from --OCN and --OH.

Under the influence of heat and/or a suitable catalyst the phenoliccyanate resin such as that of formula II and preferably formula IIIreacts to form a phenolic cyanate-phenolic triazine precursor which isuseful to form fibers. Such a precursor derived from formula III has theformula IV ##STR9## wherein Z is defined as above and r and s are 0 oran integer of one or more. Up to 80 mole percent of the cyanato groupsreact to form triazine groups in the precursor.

Fibers can be formed by meltspinning from the phenolic cyanate-phenolictriazine precursor and reacted to form phenolic-triazine fiber.##STR10##

The advancement over the art is that the resin of the present inventionis stable and has a long shelf life. This is indicated by the gel timeof greater than 1 minute, and preferably greater than 2 minutes at 155°C. The most preferred range is from 3 to 10 minutes at 155° C. Ranges ofgel times greater than 10 minutes can be used. The phenolic cyanatoresin can cure to form phenolic triazine resin which can becharacterized as having a thermal stability indicated by a thermaldecomposition temperature of at least 400° C. and preferably of at least450° C. as measured by Thermal Gravimetric Analysis (TGA).

The cyanato group containing phenolic resin of the present inventionpreferably has a number average molecular weight of from about 280 to1500, preferably 320 to about 1500, more preferably about 500 to 1000and 320 to about 1500, more preferably about 500 to 1000 and mostpreferably about 600 to 1000.

The present invention includes a fiber comprising completely as well asincompletely cured phenolic triazine resin derived from the cyanatogroup containing phenolic resin described above. Typically, the phenolictriazine is formed by heating the cyanato group containing phenolicresin.

The present invention includes a method of making fiber from the cyanatogroup containing phenolic resin of the formula II, or phenoliccyanate-phenolic triazine precursor such as the preferred precursor offormula IV. The improvement of the method of the present invention isthat the cyanato group containing phenolic resin is formed by firstreacting a phenolic novolac resin and a base, preferably trialkyl aminein a cyclic ether solvent to form a trialkylammonium salt of novolac.This step is then followed by reacting the trialkylammonium salt with acyanogen halide in the cyclic ether to form the cyanato group containingphenolic resin. It is particularly preferred to conduct the reaction ata temperature below about -5° C. and preferably from -5° C. to -45° C.,more preferably -5° C. to -30° C. and most preferably -15° C. to -30° C.

The fibers of the present invention can be formed by suitable methodssuch as solution spinning and melt spinning using conventional equipmentavailable for spinning phenolic fibers known in the art. Preferably, thefibers are melt-spun by heating the phenolic cyanate to above itsmelting point and spinning the fibers. The phenolic cyanate fiber can beincompletely cured and melt-spun. The melt-spun phenolic cyanate orincompletely cured phenolic cyanate resin fiber can then be crosslinkedto form a completely cured or more completely cured phenolic triazine.This is typically done at a temperature range of from 100° C. to 320° C.and preferably 120° C. to 280° C. and most preferably at about 240° C.to 260° C. The fibers are thermally stable upon complete curing.

The phenolic-triazine fibers can be used as chopped fiber in place offiberglass or asbestos. The fiber can be made into cord, cloth or othertextile articles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a fiber comprising a cyanato group containingphenolic resin; a fiber comprising a phenolic triazine resin derivedtherefrom; and a method to make the fiber. The present inventionincludes fibers made from incompletely cured cyanato group containingphenolic resins, also referred to as precursors, or phenoliccyanate-phenolic triazine resin.

The cyanato group containing phenolic resins, phenolic triazines, andincompletely cured cyanato group containing phenolic resins from whichthe fibers of the present invention can be made, include those describedin U.S. Ser. No. 104,700 as well as U.S. Ser. No. 041,018 both herebyincorporated by reference. The phenolic resins useful in the presentinvention can be partially cyanated. Preferably, substantially all ofthe phenol groups are cyanated.

The cyanato group containing phenolic useful in the fiber of resin ofthe present invention has improved gel time and long shelf life. It haslow volatiles, and excellent char yield and thermal properties.

The present invention is a fiber comprising a cyanato group containingphenolic resin. The cyanato group containing resin (phenolic cyanateresin) is derived from a phenolic resin comprising a repeating unit ofthe formula I: ##STR11## wherein n is 0 or an integer of one or more,and X is a radical selected from the group consisting of: --CH₂ --,--CO--, --SO₂ --, ##STR12## R is the same or different and is selectedfrom the group consisting of hydrogen and methyl radicals.

The cyanato group containing phenolic resin is derived from the phenolicresin (formula I) and has repeating units of the formula II ##STR13##wherein p is 0 or an integer of one or more,

q is 0 or an integer of one or more, and

X and R are defined as in formula I.

There is from 10 to 100 mole percent, preferably 50 100 mole percent,more preferrably 80 to 100 mole percent and most preferrably 85 to 100mole percent of the cyanate units. The phenolic units and cyanato unitscan be distributed in any order, including random or block distributionalong the polymer chain.

Formula II with end groups which are typically used is shown as formulaIIA ##STR14## wherein Z is selected from --OCN and OH.

A preferred phenolic cyanate useful to make fibers has the formula III##STR15## wherein Z is selected from --OCN and --OH.

Under the influence of heat and/or a suitable catalyst the phenoliccyanate, resin such as that formula II and preferably formula III reactsto form a phenolic cyanate-triazine precursor which is useful to formfibers. Such a precursor derived from formula III has the formula IV##STR16## wherein Z is defined as above and r and s are 0 or an integerof one or more. Up to 80 mole percent of the cyanto groups react to formtriazine groups in the precursor.

Fibers can be formed by meltspinning from the phenolic cyanate-phenolictriazine precursor and reacted to form phenolic-triazine fiber.##STR17##

The resin has a gel time as measured by the Hot Plate Stroke cure Method(see Examples) of greater than 1 minute, preferably 2 minutes, morepreferably greater than 3 minutes, and most preferably from 3 to 10minutes at 155° C. Resin with gel time ranges greater than 10 minutescan be used. Resin with gel times of greater than 20 minutes can be usedbut result in slower curing fiber.

An alternate way of measuring the stability of the cyanto groupcontaining phenolic resin by the resin being capable of forming aphenolic triazine resin having the thermal stability of at least 400° C.and preferably of at least 450° C. as measured by Thermal GravimetricAnalysis (TGA) (see Examples). The thermal stability of the compositionsis measured by TGA by heating the sample at 10° C./min and determiningthe polymer decomposition temperature. The polymer decompositiontemperature is the temperature at which the maximum rate of weight lossoccurs. The phenolic triazine resin of the present invention has a charvalue at 900° C. of at least 50% by weight, preferably from 50 to 70% byweight, and more preferably 60 to 70% by weight.

It is believed that the improved properties of the phenolic cyanateresin for use in the fiber of the present invention are attributed tothe resin having a residual amount of a dialkyl cyanamide, typicallydiethyl cyanamide of less than 2% by weight, preferably less than 1% byweight and most preferably substantially none. The diethyl cyanamide isundesirable because it generates smoke upon curing.

Preferably the cyanato group containing phenolic resin has a residualamount of phenyl cyanate of less than 2% by weight and preferably lessthan 1% by weight and most preferably less than 0.5% by weight. This isdesirable since it has been found that the phenol cyanate is a volatilematerial than contributes to thermal instability and the formation ofsmoke during curing the resin.

The cyanato group containing phenolic resin for use in the fiber of thepresent invention results in satisfactory cured triazine materialsregardless of molecular weight. The preferred molecular weight range isa number average molecular weight of 280 to 1500, preferably 320 toabout 1500, more preferably about 500 to 1000 and most preferably fromabout 700 to 1000. The molecular weight distribution and number averagemolecular weight of the cyanato group containing phenolic resin can bedetermined by gel permeation chromatography (GPC) using tetrahydrofuranas a solvent.

The cyanato group containing phenolic resins forms a phenolic triazinenetwork upon heating and/or in the presence of a curing agent. Typicalcuring conditions are from 150° to 250°C. under atmospheric or elevatedpressures which can be up to 500 psi or higher for 0.1 to 1 hourdepending on sample size. The high density of cross linkage of the curedproducts results in excellent characteristics including thermalproperties and a glass transition temperature of 300° C. or higher.

The cyanato group containing phenolic resins useful in fibers of thepresent invention react by "cyclotrimerization" of the cyanato groups ofthe copolymer to varying degrees. As used herein a "completely cured"phenolic cyanate resin forms a phenol triazine polymer in which up to 80mole percent of the cyanator group have reacted to form triazine groupsleaving less than about 20 mole percent of the original cyanato groupsremain unreacted, i.e., uncyclotrimerized, as determined by the methodof Infrared Spectrophotometry (IR). A precursor also referred to as"partially cured" or "incompletely cured" triazine is one in which from40 up to about 80 mole percent of the original cyanato groups areunreacted.

The cyanato group containing phenolic resin of the present invention isderived from a phenolic novolac. Useful phenolic novolac resins areknown in the art. A typical and useful one is disclosed in U.S. Pat. No.4,022,755 at column 2 beginning at line 27. Particularly useful phenolsinclude phenol, cresol and xylenol.

The present invention includes a method to make the fiber comprising thecyanato group containing phenolic resin recited above. This involves thesteps of reacting novolac resin and a trialkyl amine in a cyclic ethersolvent to form the trialkylammonium salt of novolac. This is followedby reacting the trialkylammonium salt with a cyanogen halide in thecyclic ether to form the cyanato group containing phenolic resin. Thereaction is conducted at a temperature range of below -5° C., preferablyfrom -5° C. to -45° C., and more preferably from -5° C. to -30° C. andmost preferably from -15° C. to -30° C.

The reaction product is in solution in the cyclic ether. This reactionproduct is a cyanato group containing phenolic resin. It is separatedfrom the solution by a suitable separation technique. The preferredtechnique is precipitation into a non solvent medium. Useful nonsolventsare a alcohols with isopropanol being preferred. The separation ispreferably conducted at atmospheric pressure. While it can be conductedat room temperature, the temperature is typically from -0° C. to -45°C., preferably -55° C. to -25° C. Precipitation is preferably conductedwith agitation.

The improved properties of the resin used to make the fiber of thepresent invention are attributed to reacting the novolac resin and atrialkyl amine in a cyclic ether solvent to form the trialkylammoniumsalt of novolac resin this is followed by reacting the trialkylammoniumsalt with a cyanogen halide in the cyclic ether to form the cyanatogroup containing phenolic resin. The reaction is conducted at belowabout -5° C., preferably to -5° C. to -45° C., more preferably from -5°C. to -30° C. and most preferably from -15° C. to -30° C.

The cyclic ether solvent has been found to be an important reactionmedium to form the cyanato group containing phenolic resin of the preseninvention. The cyclic ether solvent is preferably selected from thegroup consisting of: tetrahydrofuran; 1,4 dioxan; and furan. Thetrialkyl amine can be selected from triethyl amine, tripropylamine andtriethylcyclohexyl amine. Additionally, the reaction medium can containother bases to control the pH to help control the rate of the reaction.

The relative amounts of solvent i.e. tetrahydrofuran, trialkylamine, andphenolic resin used should be controlled to control gel time of thecyanato group containing phenolic resin. Concentrations can be measuredas a function of the weight percent of the trialkyammonium salt whichcould theoretically be calculated based on the weight of thetrialkylamine, phenolic resin and solvent. Preferably, the amount oftrialkylammonium salt is from 5 to 35, more preferably 10 to 25, andmost preferably from 10 to 20 percent by weight. The preferredconcentration can vary depending on the specific solvents and reactantsused.

A preferred phenolic cyanate resin useful to make the fiber of thepresent invention begins with a phenolic novolac backbone. This isreacted with cyanogen halide such as cyanogen bromide (CNBr) in presenceof an organic base, such as triethylamine (Et₃ N) in a solvent such astetrahydrofuran (THF) to form phenolic cyanate ##STR18## Under theinfluence of heat and/or a suitable catalyst phenolic-cyanate formsphenolic cyanate-phenolic triazine precursor. ##STR19##

Fibers can be formed by meltspinning from the phenolic cyanate-phenolictriazine precursor to form phenolic-triazine fiber. ##STR20## Bothtriazine and cyanate ester formation deactivate the benzene nucleus andthus inhibits peroxide formation at the methylene linkage, through bothsteric and inductive effects. Thermal and oxidative stability isenhanced and the possibility of afterglow or punking is deminished. Inaddition to thermal and oxidative stability, the mechanical propertiesis substantially improved through the contribution of the ether andtriazine bridge.

The fibers of the present invention made of cyanato group containingphenolic resin or phenolic triazine resin can be made in suitable waysto make fibers. The preferred methods include melt spinning and solutionspinning. Useful ways to make fibers are described in U.S. Pat. No.4,076,692, hereby incorporated by reference. Briefly the resin is meltedprior to fiberizing. However, because of the stability of the cyanatogroup containing phenolic resin of the present invention the concernabout fiberizing in a relatively fast time after melting expressed inU.S. Pat. No. 4,076,692 is not as critical. The phenolic cyanate resinof the present invention can be spun or can first be incompletely curedand then spun. Typically, the resin is heated to a temperature of from100° C. to 120° C., preferably. Unlike the spinning of conventionalnovalac resins where the upper temperature limitation is criticalbecause of the decomposition of that resin at a temperature of 350° C.,the present invention is directed to a triazine resin which forms and isstable at very high temperatures up to 470° C. and typically 420° C. to450° C.

The melted resin can be fiberized by any suitable means includingrapidly extruding resin through a heated dye, centrifically spinningfibers from the melt resin, and blowing fibers from the melt resin witha compressed gas such as compressed air. A particularly suitablelaboratory method is by using a Instron® Capillary Rheometer.

After the fibers are formed they can be used in their incompletely curedstate or they can be completely cured by heating. Although the curingcan be catalyzed, it is preferred to cure the fibers by simply heatingto the temperature ranges recited above for forming the triazine resinfrom the cyanato containing phenol resin.

The fibers of the present invention particularly in the phenolictriazine form are stable at high temperatures in ranges up to 420° C. to470° C. they are useful in applications such as reinforcing fillers forfriction resistant components such as for use in brakes and gaskets.They are also useful as an asbestos replacement. The fibers are suefulin chopped form suitable in lengths, typically from 1/16 inch to 1 inchin length. Alternatively the fiber can be used to make yarn, cord orrope. The fibers can be formed into fabric by suitable textileprocessing.

The chopped fiber can be used in place of chopped glass or asbestosfibers. Compositions can comprise the chopped fibers and thermosettingresins or thermoplastic polymers. The fiber can be used as a frictionresistant filler in place of asbestos in compositions for use as brakes,clutches, and the like.

The recent trend in automotive brake system is to use non-asbestos basedformulation for friction material. Phenolic-triazine fiber is derivedfrom phenolic novolac. Phenolic novolac resin is commonly used as abinder in friction compositions. Fiber made of phenolic triazine hassimilar chemical structure and as novolac resin will enhance theprocessing operation in frictional composites.

Woven and knit fabric can be made. The thermal stability and flameresistance of the phenolic triazine makes cloth from this fiber usefulin a variety of applications where flame resistance is important. Thisfiber can be used in flame resistant clothing, curtains and the like.

Several examples are set forth below to illustrate the nature of theinvention and method of carrying it out. However, the invention shouldnot be considered as being limited to the details thereof. All parts areby weight unless otherwise indicated.

SAMPLE TESTING

Measurements were made to determine the gel time of the cyanatocontaining phenolic resins produced by Examples 1 through 3 of thepresent invention as well as the comparative examples. The samples weretested for gel time using the following procedure:

Apparatus

Stop watch

0°-250° C. thermometer

Electric hot plate, adjusted to 155±1° C. and enclosed in a wind shield

4" Spatula

Method

1. For powdered resins: Weigh out a 1.0 gram sample on a watch glass.

2. Quickly dump the complete sample on the center surface of the hotplate and at the same time start the stop watch.

3. Using a 4" spatula spread the resin over a 2 inch square area in thecenter of the hot plate and stroke the entire area with the spatula at arate approximating 80 strokes per minute. Without stopping the watch,note the time it took for the resin to melt.

4. Continue stroking, keeping the blade of the spatula close to thesurface of the resin, until the resin has passed through a stringy stageand suddenly seems hard and glazed and offers little or no resistance tostroking with the spatula. This end point is best determined only afterconsiderable practice to get the "feel" of the resin as it "lets go" atits gel point.

5. Record number of seconds to melt and number of seconds for gel time(cure time). Subsequent checks on the same sample should agree within ±5seconds.

Smoke generation was a visual observation during testing of gel time. Asatisfactory material will substantially have no smoke or vaporgeneration during gel measurement at 155° C. The material used in theExamples was satisfactory.

EXAMPLE 1 Preparation of the Phenolic Cyanate Resin

A mixture of 204 g of novolac (630 number average molecular weight) and202 g triethylamine was dissolved in 0.8 liters of tetrahydrofuran (THF)at ambient temperature to form a triethyl ammonium salt of novolac. A222 g sample of cyanogen-bromide was dissolved in 1.2 liters oftetrahydrofuran under nitrogen atmosphere. The solution containing thetriethylammonium salt of novolac was added to cyanogen bromide solutionover a period of one to 11/2 hours. During the addition, the temperatureof the reaction mixture was maintained at -15° to -20° C. After theaddition was completed, the reaction mixture was stirred for additionalan 18 hours and the temperature of reaction mixture rose to about -2° C.to -5° C. The mixture was warmed to room temperature. The product wasisolated by filtration to remove triethylammonium bromide salt. Thefiltrate was purified by precipitation in a cold isopropanol (-30° C.)and a white precipitate was isolated. The white precipitate which is thepolymer, was redissolved in THF and precipitated again. The product wassubsequently dried overnight to produce an off white phenolic cyanateresin as indicated by Infrared Spectrum. Infrared Spectra also indicatedthe presence of 5% free phenolic groups. The gel time was 3 minutes at155° C.

The phenolic cyanate was melted on aluminum foil at 100° C. for 15minutes under 30 inches of Hg to obtain a phenolic cyanate-phenolictriazine precursor (incompletely reacted phenolic cyanate). Theprecursor was melted to 125° C. and fibers were drawn with a glass rod.The fibers were cured at 250° C. for about one half hour.

The fibers were tested to determine the oxidative stability using theThermal Gravimetric Analysis (TGA). The samples were heated at 10°C./min from 0° C. in air. Sample size was from 30 to 40 mgs. Comparative1 was a phenolic formaldehyde resin fiber XF02BT produced by NipponKynol. Comparative 2 was Kevlar® polyaramid pulp (short fibers) made bythe DuPont Company. The initial weight loss for the samples ofComparatives 1 and 2 up to 200° C. may be due to moisture loss. Theresults of the TGA are summarized in Table 1 which follows:

                  TABLE 1                                                         ______________________________________                                                             Comp 1                                                   Material   Ex 1      Phenolic    Comp 2                                       % Wt loss @                                                                              PT        Formaldehyde                                                                              Kevlar                                       ______________________________________                                        100° C.                                                                           0         4           4                                            200        0         4           4                                            300        0         5           4                                            400        0         14          5                                            500        19        79          10                                           600        29        99          100                                          ______________________________________                                    

EXAMPLE 2 Preparation of the Phenolic Cyanate

A mixture of 204 g of novalac (613 number average molecular weight) and212 g triethylamine was dissolved in one liter of tetrahydrofuran atambient temperature for form a triehtyl ammonium salt of novolac. A 240g sample of cyanogen bromide was dissolved in one liter oftetrahydrofuran under nitrogen atmosphere. The solution containing thetrimethylammonium salt of novolac was added to cyanogen bromide solutionwith a average addition rate 7-8 ml/min. During the addition, thetemperature of the reaction mixture was maintained at -20° to -30° C.After the reaction was completed, the reaction was allowed to continuefor additional one hour to bring the temperature of reaction mixture to+10° C. The product was isolated by filtration to removetriethylammonium salt. The filtrate was purified by precipitation in acold isopropanol/dry ice mixture (-15° C. to -20° C.) (twice), andsubsequently dried in a vacuum overnight to produce an off whichphenolic cyanate. The elemental analysis indicated: wt% C=73.5 (73.5),wt% H=4.0 (3.82), and wt% N=10.6 (10.7). The numbers in parentheses aretheoretical values. The elemental analysis is based on the empiricalformula of the phenolic cyanate unit, C₈ H₆ NO. The IR Spectrum indictedabsorption at --C═N (22.50(m-¹) and absence of any carbamate. The gaschromatographic (GC) analysis showed absence of diethyl cyanamide. Thegel time was 30 minutes at 155° C.

Intermediate (Precursor)

A 50 cm sample was spread onto aluminum foil and placed in a preheatedvacuum oven at 125° C. for 30 minutes under 30 inches of Hg pressure.The material melted under this condition. The material was cooled toroom temperature and ground to a fine powder. From IR Spectrum about 10%of the cyanate groups were converted to triazine groups.

The precursor was formed into fiber using a Instron® CapillaryRheometer. The die used was 0.225 inches long, and 0.015 inches indiameter. The resin was fed into the die at 55° C. at a pressure of 20psi. A vacuum was applied to remove trapped air, prior to compaction.The temperature was increased to 145° C. and held for 8 minutes prior toextrusion. The flow observed was irregular as indicated by a shear raterange of 130-1300 sec-1. A more stable extrusion rate is expected byvarying conditions such as increasing the temperature, and varying time.The fiber was drawn from the die at 145° C. and taken up onto a coolingroll at about room temperature. The fiber was white. The cooled fiberwas stored on a spool.

Samples of the fiber were then cured in oven in air for 1/2 hour at 80°C., 1 hour at 100° C., 11/2 hour at 150° C., 2 hours at 200° C. and 1hour at 250° C. After curing the fiber light yellow, the fiber appearedto be satisfactory to handle and in appearance.

EXAMPLE 3

A mixture of 50 grams of novolac (613 number average molecular weight)and 51.0 grams of triethylamine was dissolved in 160 grams oftetrahydrofuran at ambient temperature to form the triethylammoniumsalt. A 53 gram sample of cyanogen bromide was dissolved in 135 grams oftetrahydrofuran under nitrogen atmosphere. The solution containing thetriethylammonium salt of novolac was added to cyanogen bromide solutionwith an average addition rate 7-8 ml/min. During the addition, thetemperature of the reaction mixture was maintained at -20° to -30° C.After the reaction was completed, the reaction mixture was stirred foran additional one hour and the temperature of the reaction mixture roseto +10° C. The product was isolated by filtration to remove triethylammonium salt. The filtrate was purified by precipitation in a coldisopropanol/dry ice mixture (-15° C. to -20° C.) (twice) andsubsequently dried in a vacuum over night at 40° C. to produce an offwhich phenolic cyanate. The gel time at 155° C. was 3 minutes. Thismaterial can be used to draw fiber in any suitable manner such used inExample 2.

While exemplary embodiments of the invention have been described, thetrue scope of the invention is to be determined from the followingclaims:

What is claimed:
 1. A fiber comprising a cyanato group containingphenolic resin comprising repeating units of the formula ##STR21##wherein p is 0 or an integer of 1 or more, q is 0 or an integer of 1 ormore, X is a radical selected from the group consisting of: --CH₂ --,--CO--, --SO₂ --, ##STR22## and R is the same or different and isselected from hydrogen and methyl groups, there being from 10 to 100mole percent cyanato units.
 2. The fiber as recited in claim 1 whereinthe resin has no smoke generation during gel time measurement.
 3. Thefiber of claim 1 wherein the resin has a gel time of greter than 1minute at 155° C.
 4. The fiber of claim 3 wherein the resin has a geltime of from 3 to 10 minutes at 155° C.
 5. The fiber as recited in claim1 wherein the cyanato group containing resin has a number averagemolecular weight of from 280 to
 1500. 6. The fiber as recited in claim 1wherein there are from 80 to 100 mole percent cyanato units.
 7. Thefiber as recited in claim 1 in the form of chopped fiber.
 8. The fiberas recited in claim 1 in the form of yarn.
 9. Fabric made of the fiberas recited in claim
 1. 10. A phenolic cyanate-phenolic triazine resinfiber derived from cyanate group containing phenolic resin recited inclaim
 1. 11. A phenolic triazine resin fiber derived from the cyanatogroup containing phenolic resin recited in claim
 1. 12. The fiber ofclaim 11 wherein the phenolic triazine resin has a thermal decompositiontemperature of at least 400° C. as measured by Thermal GravimetricAnalysis.
 13. The fiber as recited in claim 1 wherein the cyanato groupcontaining resin has the formula: ##STR23## wherein Z is selected from--OH and --OCN.
 14. A fiber comprising a phenolic triazine resin derivedfrom a cyanato group containing phenolic resin comprising repeatingunits of the formula ##STR24## wherein p is 0 or an integer of 1 ormore, q is 0 or an integer of 1 or more, X is a radical selected fromthe group consisting of: --CH₂ --, --CO--, --SO₂ --, ##STR25## and R isthe same or different and is selected from hydrogen and methyl groupsthere being from 10 to 100 mole percent cyanato groups.
 15. The fiber ofclaim 14 wherein the phenolic triazine resin has thermal decompositiontemperature of at least 400° C. as measured by Thermal GravimetricAnalysis.
 16. The fiber as recited in claim 14 wherein the phenolictriazine resin has a char yield of at least 50% by weight at 900° C. 17.The fiber as recited in claim 14 wherein the phenolic triazine resin isderived from a cyanto group containing phenolic resin having a gel timeof greater than 1 minute and substantially no smoke generation duringgel time measurement.
 18. The fiber as recited in claim 14 wherein atleast 80 mole percent of the cyanato group reacted to form triazinegroups.
 19. The fiber as recited in claim 14 in the form of choppedfiber.
 20. The fiber as recited in claim 14 in the form of yarn. 21.Fabric made of the fiber as recited in claim
 14. 22. The fiber asrecited in claim 14 wherein the cyanato group containing resin has theformula ##STR26##